Repair diagnoses cost

"One of the ribbon cables was damaged when i was trying to replace the thermal paste so that needs replaced since i believe thats why it won't turn on anymore, but the main issue asides that is the constant crashing, for the last year it's progressively got worse where on any heavy duty games the console itself will completely turn off or it'll return to the home screen every 5-60 mins, i replaced the thermal paste and it didn't change anything so i don't think it's overheating" that's the message/summary i sent the repair shop, ive had the series x for almost 5 years, does anyone have any idea what the issue may be incase i should get a new xbox, or even an idea of what this kind of repair may cost thanks